When running AB or MVT tests on the IR experiment module, the platform will need to split your selected product segment into 2 groups for testing purposes - Group A and Group B.
When setting up your experiment it will default to the Random Sort method but if you want to ensure that the distribution of products between the 2 groups is more ordered then you can choose to Sort & Assign.
This will then allow you to choose to order your products by one of your performance metrics, so you could sort them by the highest Clicks, Revenue, Impressions, CTR etc. This ensures you don't end up with your top performers all in one of the groups thus skewing the results and meaning the learnings are flawed. Just click on the dropdown to select the metric you want to use.
If you have the Google Ads Data connector you can now sort & assign by google impressions or you can use the metrics to filter your set of products for the experiment in the first place.
It's very much like being ordered by height before being separated into teams when you were at Junior School, to ensure all the bigger children weren't in one team :)